The present invention relates generally to transmissions for use in four-wheel drive vehicles. More particularly, the present invention is directed to a transmission having a multi-speed geartrain and a power transfer mechanism contained in a single unit.
As is known, the majority of four-wheel drive vehicles are equipped with a transfer case mounted to a multi-speed transmission for directing power from the engine to all four wheels. To accommodate different road surfaces and conditions, many transfer cases are equipped with a mode shift mechanism which permits the vehicle operator to selectively couple the non-driven wheels to the driven wheels for establishing a part-time four-wheel drive mode in addition to the two-wheel drive mode. Other transfer cases are equipped with a transfer clutch that is passively or actively controlled in response to driveline slip for automatically delivering drive torque to the non-driven wheels and establishing an on-demand four-wheel drive mode. In addition, some transfer cases are also equipped with a two-speed range shift mechanism for permitting the vehicle operator to select between a high-range and a low-range four-wheel drive mode.
In an effort to minimize the overall size of the drivetrain used in four-wheel drive vehicles, it has been proposed to utilize a transmission of a transaxle-type normally used to drive the front wheels of a front wheel drive vehicle as a four-wheel drive geartrain. In particular, British Patent No. 2,035,930 to Jones et al. teaches of rotating the front wheel drivetrain (i.e., engine and transaxle) 90.degree. such that the transaxle outputs can be interconnected to the front and rear drivelines of the motor vehicle. While such an arrangement may provide an economical drivetrain layout for a full-time four-wheel drive vehicle, the practical applications for such an arrangement are severely limited. In particular, such an arrangement does not permit the vehicle operator to selectively shift "on-the-fly" between high and low four-wheel drive modes, nor can one of the outputs be selectively disconnected from its driveline for establishing a two-wheel drive mode.
Accordingly, the need exists for a transmission which can be used in most conventional four-wheel drive applications and which permits the vehicle operator to selectively shift between the available drive modes and speed ranges.